Low gloss hybrid powder coating

ABSTRACT

A curable powder coating composition comprising one or more hydroxyl or carboxyl functional polyester(s) (A), one or more hydroxyl or carboxyl functional acrylic resin(s) (B), one or more cross linker(s) (C) able to react with (A) and/or (B).

FIELD OF THE INVENTION

The present invention relates to powder coating formulations,particularly powder coating compositions having improved chemicalresistance and matte surfaces.

BACKGROUND

The desire for resilient powder coatings is becoming increasinglypopular. Today, there are well known basic powder chemistries that havebeen utilized over the past several decades that meet standarddurability requirements. However, most powder chemistries available inthe current industry are not equipped with the appropriate chemicalmakeup for extreme situations or environments. As this form ofultra-durable powder coating becomes more prevalent, innovations of thechemical makeup of typical powder coating chemistries is in high demand.

Today, there are several well-known chemical makeups known in theindustry that are defined as durable powder coatings. Examples of knowndurable powder chemistries include: polyester, polyester/isocyanate,acrylic and fluoropolymer powder coatings. More than 60 percent of themarket utilizes polyester-based coatings, which are equipped to withholda measureable amount of standard outdoor environments such as corrosionand ultra-violet light exposure. Depending on the specifications thesepowder coatings are available in a wide gloss range from high-gloss todull-matte finish. However, when these coatings are exposed to chemical,biological or decontaminating reagents, they are unable to withstandsuch harsh environments.

U.S. Pat. No. 9,206,320 B1 relates to matte-appearancechemical-agent-resistant powder coating compositions, which comprise aresin component, a polyisocyanate-containing uretdione cross-linkingagent, a catalyst, and a flattening agent. The resin component maycomprise a hydroxyl-containing resin and a hydroxyl-containinghalogenated copolymer resin. Catalyzed cross-linking of the uretdioneisocyanate groups and resins of the resin component during curingpreferably is disclosed to yield a finished-form film with low levels ofgloss and sheen and chemical-agent resistance.

U.S. Pat. No. 9,012,556 B1 describes low reflectance chemical agentresistant coating compositions comprising a first acrylic powder resinhaving a hydroxyl value of at least about 180, a second acrylic powderresin having a hydroxyl value less than about 45, a crosslinker reactivewith the hydroxyl functional acrylic resins and wollastonite.

U.S. Pat. No. 8,969,577 B2 is directed to curable compositionscomprising a thermolatent amidine base and an organic material which ispolymerizable or crosslinkable with a basic or nucleophilic catalyst. Inparticular, the document describes curable coating compositions,especially powder coating compositions, and curable adhesivecompositions, as well as the use of a thermolatent amidine base as acuring catalyst for thermally induced base-catalyzed polymerization orcrosslinking reactions. The polymerizable or crosslinkable organicmaterial may be a two-component system comprising a hydroxylgroup-containing polyacrylate and/or polyester and an aliphatic oraromatic polyisocyanate.

SUMMARY OF THE INVENTION

The present invention relates to a curable, dull-matte, powder coatingcomposition, accommodating superior chemical resistance through a uniqueand innovative complex of hydroxyl-functional polyesters andacrylic-copolymers that are cross-linked through the utilization ofisocyanates—preferably blocked isocyanates—and/or other suitable curingagents. It provides a system which shows a high chemical resistance incombination with good mechanical flexibility. Furthermore, in a specialand preferred version of the present invention, fluorinated resins ororganic compounds are added to the composition. In particular thiscomplex, with the addition of various PFA (perfluoroalkoxy polymers)and/or polytetrafluoroethylene (PTFE) additives, implements optimaldurability, survivability and chemical agent resistant absorbance; whilemaintaining a matte surface. The present invention ultimately yields acutting edge, hybrid powder coating that enables any coated surface tosustain durability in vast environments and to resist absorption ofchemical, biological and decontaminating reagents if and when exposedto. In special and preferred embodiments of the present invention thefinal powder coating material can even lead to a coated surface withsuch an improved resistance to chemical, biological and decontaminatingreagents, e.g., mustard gas, that the specification MIL-PRF-32348 can befulfilled.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates extrudate with 3% high molecular PTFE.

FIG. 2 illustrates a negative result on flexibility test (Example 2).

FIG. 3 illustrates a positive result on flexibility test (Example 12).

FIG. 4 illustrates a negative result on DS2 Test (Rate 3).

FIG. 5 illustrates a positive result on DS2 test (Rate 1).

DETAILED DESCRIPTION OF THE INVENTION

Slight variations above and below the given ranges can be used toachieve substantially the same results.

With regard to the present invention and especially concerning theaccompanying claims, it is understood that any combination of thesubject matter of the different claims falls under the idea and thefollowing disclosure of the present invention, although the subclaimsare, for formal reasons, been made dependent from the main claim only.

According to the present invention, a highly saturated hydroxyl orcarboxyl-functional polyester resin component can serve as thefunctional binder of the powder coating. The invention is not limited toa special polyester formulation. Typical examples of the acid componentinclude, but are not restricted to terephthalic acid, isophthalic acid,trimellitic acid, adipic acid, polybasic acids and pyromellitic acid, toname a few. Typical examples of the alcohol component include, but arenot restricted to: ethylene glycol, 1,4-butanediol, 1,6-hexanediol andneopentyl glycol. The used polyester can be hydroxyl-,carboxyl-functional or a combination thereof in one or more polyesters.

Some typical polyesters and monomers for such polyesters can be found inU.S. Pat. No. 9,206,320 B1 and EP 1 848 782 B1.

Also unsaturated monomers like alcohols and acids can be used for theinvention.

A preferred hydroxyl-functional polyester resin has a density of about1.2 g/cm³, an hydroxyl value of about 10 to 350, preferably between 200and 250 mg KOH/g and a Tg above 30° C. and is produced by polymerizationof at least one acid component and at least one alcohol component.

Suitable monomers of polyesters and/or polyesters are well known in thefield and are for example listed in U.S. Pat. No. 9,206,320 B1.

For the present invention, the hydroxyl or carboxyl-functionalpolyester(s) (A) are then reacted with one or more hydroxyl orcarboxyl-acrylic copolymer resin(s), having a Tg above 30° C.Surprisingly it was found that hydroxyl or carboxyl-acrylic (co)polymer(B) based resins can implement high chemical resistance together with amatt appearance when combined with hydroxyl or carboxyl functionalpolyester-resins to formulate powder coatings, as long as the amount offunctional groups in the hydroxyl- or carboxyl-acrylic copolymer and thehydroxyl or carboxyl functional polyester resin differs significantlyand furthermore not only a certain low gloss level but also stillsufficient mechanical flexibility can be achieved. Furthermore it wassurprisingly found that for a matt appearance the combination of acrylicand polyester resin with approximately the same difference in acid orhydroxyl-value give a higher gloss reduction compared to a combinationof polyester/polyester or acrylic/acrylic. The difference of functionalgroup value(s) between the hydroxyl or carboxyl-functional polyester andhydroxyl or carboxyl-acrylic copolymer(s) should be greater than orequal to 30.

Suitable monomers of acryl resins and/or acryl resins are well known inthe field and are for example listed in U.S. Pat. No. 9,012,556 B1 andor in U.S. Pat. No. 9,206,320 B1. The used acrylic resins can behydroxyl-, carboxyl-functional or a combination thereof in one or morepolyesters. Also the use of epoxy/GMA groups in the acrylic resin isoptional.

The powder coating composition according to this invention furthercomprises one or more crosslinker(s) able to react with the functionalgroups of the polyester and/or acrylic resins used, such as blockedisocyanates, uretdiones, cyclic-amide and/or multi-acid compounds toname a few. For a better chemical stability blocked isocyanates arepreferred compared to blocked uretdiones. Also glycolurile are suitableoption in such cases. Such a combination according to the inventiontaken can produce a chemical resistant powder coating with glossvalues≤35 (as can be seen from the following examples like 1, 4, 5, 6and 9) measured at a 60° angle. Critically defined by the combination of(A) and (B), the invention at hand has the ability to provide a powdercoating, that is able to create a dull-matte finish with a gloss valueunder 10, measured at 60°. With the addition of other raw materials, themeasured gloss value may vary accordingly, in either direction. Suitablecrosslinkers are well known in the field and are for example listed inU.S. Pat. No. 9,012,556 B1 and in U.S. Pat. No. 9,206,320 B1.

In some embodiments of the present invention, a blocked cycloaliphaticpolyisocyanate is used as crosslinker. In one embodiment a ε-caprolactamblocked trimethylolpropane 4,4′-methylene dicyclohexyl diisocyanate(H12MDI) adduct, with a Tg of 55° C., is used to react with anotherhardener component in conjunction with a hydroxyl or carboxyl-functionalpolyester resin and a hydroxyl or carboxyl-acrylic-copolymer to formexterior durable polyurethanes. Said raw material exhibits fasterreactivity, better hardness and flexibility than conventional isophoroneisocyanate adducts. The preferred blocked cycloaliphatic polyisocyanateshould have an NCO % of about 14.0, contain a functionality of 2.2, andhave a Tg value near or about 60° C.

In another embodiment of the invention ε-caprolactam blockedtrimethylolpropane isophorone diisocyanate adduct, which should containa cyclic amide or caproic acid, having a Tg value of or near 52° C., isused to crosslink hydroxyl functional groups of polyester and acryliccopolymer-based resins. The addition of blocked polyisocyanate adductpolyols has an influence on the mechanical performance of the powdercoating, and the blocked polyisocyanate remains stable during processingup to the unblocking temperatures of more than 160° C. The amount ofpolyisocyanate derivative can vary from 1 to 50 percent by weight of thetotal powder coating composition.

Principle Isocyanate Reaction with Alcohol to Produce an Urethane

In another preferred embodiment of the present invention, a polymer witha melting area of 50° C. to 200° C., preferably 100 to 150° C. and aviscosity of 10 to 500 Pas, preferably 50 to 250 Pas and most preferably90 to 150 Pas at 200° C., measured with plate/plate viscometer at ashear rate of 10 rad/s, is added.

GRILTEX ES 502 as copolyester is a suitable compound which modifies theGardner Impact Efficiency as well as the flexibility in accordance withASTM D522 (Mandrel Bend Test of Attached Organic Coatings). The MandrelBend Test according ASTM D522 (Method B using a ¼ inch mandrel) is anintegral part of the MIL-PRF-32348. Alternative impact modifiers areacrylic based modifiers which offers not only the impact modifierfunction it offers also a multifunctional combination between impact andweather ability.

In yet another embodiment of the present invention, the hardener (C) inthe system comprises one or more carboxylic acid(s) and/or salt(s) ofcarboxylic acid(s) containing hardeners present in aweight-concentration of below or equal to 50%, preferably below or equalto 20% and most preferably below or equal to 15% of (C). Surprisingly itwas found that with that adding that kind of material into the hardenersystem C allows further gloss reductions even at an already low level ofgloss.

Especially the combination from dicarboxylic acids such as nonanedioicacid, decanedioic acid, undecanedioic acid preferably dodecanedioic acidwith a compound from 1,2,4,5 benzenetetracarboxylic acid with2-phenyl-2-imidazoline pyromellitate (1:1) (CAS 54553-90-1) waspreferred as this showed an additional gloss reduction even at a glosslevel in the range below 3 (measured at 60° angle).

In a special embodiment of the present invention, the combination fromdicarboxylic acids such as nonanedioic acid, decanedioic acid,undecanedioic acid preferably dodecanedioic acid with melamine was alsosurprisingly found to have an addition gloss reduction effect at verylow gloss levels in the range below 3 (measured at 60° angle).

Depending on the color and the associated pigment volume concentration,different filler types, for further gloss reduction, can be used whichare commonly known in the field of powder coatings. However, coarsebarium sulfate and/or preferably kaolinite in combination withrheological modifiers such as derivatives of smectite clay were found tohave a very effective gloss reduction effect.

According to the present invention, flow control agents may be added tothe formulation in an amount preferably from 0-15 percent by weight ofthe total powder composition. In one embodiment, a carboxyl functionalacrylic polymer product, which has been converted into free-flowingpowder by adsorption onto silica-type carrier, provides excellentre-coatability, clarity and appearance.

According to the present invention, also degassing agents may be addedto the formulation, if needed or preferred. Suitable agents are forinstance benzoin (preferred), and alternative or in combination forexample be Powdermate 542 DG from Estron Chemical can be used.

The utilization or non-utilization of pigments, whether organic- orinorganic-based, can be implemented into the present invention, alsoregarding the requirements of the MIL-PRF-32348 specification. Suchsuitable/non-suitable pigments include, but are not limited to titaniumdioxides, antimony oxides, chromium oxides, zinc oxides, calciumcarbonates, fumed silicas and zinc phosphates, to name a few. Inaddition, different forms of fillers, including, but not limited to,barium sulfates (e.g., barytes) and/or calcium carbonate, can be used aswell.

The addition of fluoro containing organic compounds (D), preferablyfluoro containing oligomers and/or polymers in a concentration ofbetween 0.5 and 19 weight percent, preferably between 1 and 10 weightpercent and most preferably between 1.5 and 3.5 weight percent based onthe sum of (A), (B) and (D) lead to a further increase in chemicalresistance. Normally a very high chemical resistance can be achieved bya very crosslinked system. However, a very crosslinked system shows amarked lack of mechanical properties. Surprisingly it was found that theaddition of a high molecular PTFE (MW>1000000) as a surface modifierincreases the performance against chemical attack. PFA (perfluoroalkoxypolymers), which is a copolymer, exhibits also good mechanicalproperties and permeation resistance. PFA is similar to PTFE but PTFE isnot melt-processable and PFA is melt-processable. This facilitates themanufacture. Additionally to this it was found that themicro-structuring effect of that kind of material additionally has apositive effect on the gloss reduction which allows achieving dull-mattcoatings. For the later also other suitable compounds like polyethyleneand PMMA (polymethylmethacrylate) with a suitable particle sizedistribution between 5 and 150 μm can be used. Additionally, the scratchresistance was found to be improved and the friction coefficient (COF)reduced by addition of these materials.

It was found that the further addition of PTFE and/or other suitablefluorocarbons like PFA can not only improve matte appearance, increasescratch resistance, improve structuring and be utilized to yield a finetextured product, but also yields powder coating compositions withimproved resistance to chemical, biological and decontaminatingreagents, e.g. mustard gas, according to MIL-PRF-32348. Considered afluorocarbon, this fluorcarbons solid has a high molecular weight andmainly consists of carbon and fluorine. It was even found that mustardgas test standards of MIL-PRF-32348 can be fulfilled. Also the additionof fluoro-polymers with functional groups suitable to react with thecrosslinkers C or at least one of the crosslinkers in C can be addedaccording to the invention. Such kind of material is for example FEVEwhich is known under the trade name Lumiflon.

In yet another embodiment of the present invention, the overall glosswas reduced using additives with a composed form of salt cyclic-amideand or multi-acid compound(s) allowing the yield product to maintainhigh mechanical strength, while having a matte, yet fine appearance.Cyclic-amide and or multi-acid solids used according to the presentinvention typically have melting point ranges between 190° C. to 240° C.The amount of cyclic-amide and or multi-acid utilized in the inventionis about 1 to 20 weight percent of the total formula composition.

Production of the Powder Coating

The powder coatings composition according to the present invention canbe produced by standard production procedures well known in the art suchas extruding the components of the coating composition, grinding of thecooled extrudate to a suitable particle size and applying the coatingpowder to suitable substrates. The application can be performed usingany method available, e.g. using electrostatic spraying guns, or byusing a fluidized bed.

For some embodiments it might be useful to produce two separate powdercoatings, one including a hydroxyl or carboxyl-functional polyesterresin, crosslinker(s) and fillers and one including a hydroxyl orcarboxyl-acrylic copolymer, crosslinker(s) and fillers, and combiningthe two separately extruded and ground powder coating compositionsbefore applying them to the substrate (known in the art as 2-componentpowder coating systems). However, based on the experiments with thepowder coating composition according to the present invention, low glosslevels up to below 1 can even be achieved via a so called 1 componentsystem.

The substrate to be coated can be provided at ambient or at elevatedtemperature.

The powder coating composition according to the present invention can,once applied, principally cured at a broad temperature range of about130° C.-250° C. for 5 to 50 min. However, a preferred curing cycle was10 min at 200° C. If necessary the substrate can be pretreated by commonmeans known in the art like sand-blasting, conversion coating etc.and/or one or more primer coatings can be applied before the substrateis coated with the inventive coating described herein.

EXAMPLES

The foregoing is illustrative of the present invention and is not to beconstrued as limiting thereof. Although a few exemplary embodiments ofthis invention have been described, those who are experienced in thefield of interest will readily appreciate that an exceptional amount ofmodifications is possible in the exemplary embodiments; not strayingfrom the core techniques and advantages of this invention. In addition,the present invention is not limited to all such modifications andembodiments disclosed. The invention is defined by the following claimsand with the claimed equivalents included as well.

If not otherwise stated, the powder coatings shown in the examples wereproduced via the following route.

Production

Blending

Pilot 3 by Thermo Prism

After weighing together the compounds of the formulation it will beblended with 1000 RPM for 1 min.

Extruder

Twin screw Extruder ZSK 18 by Coperion

Temperature Zones: 60, 80, 100, 120, 120 [° C.]

Screw configuration: Standard configuration (see page 6)

Feeder: Torque 30-40% at 600RPM

As the extrudate leaves the extruder with 120-140° C., the mass has moreof a thermoplastic behavior (see picture below) than usual formulations.Especially when high molecular polytetrafluoroethylene (Dyneon TFM 1750PTFE or Fluo 750FX) or perfluoroalkoxy polymers (Hyflon PFA P7010) whereused in the formulations. If more than 1% is used then the chips need tobe cooled down in a freezer after the production or else they will notbreak but just be deformed by using a blunt object to break them likeusually. In certain formulations it is necessary to reach down to atleast 5-10° C. with the cooling drums or else the extrudate will stickto the cooling drums or band.

Milling

ICM 2.4

The chips for the milling should be approximately 1 cm³ or smaller inorder to guarantee a good transportation inside the mill. Thetemperature of the air inside the mill should not exceed 15° C.otherwise the particles will be stuck on the lower half of the cyclonewall. The speed of the mill must be set high enough in particular forthe almost thermoplastic chips to break. The particles need to be smallenough to produce a closed surface.

Particle Size Distribution

PSD Measuring instrument: Mastersizer 2000

Dry-Dispers unit: Scirocco 2000

After milling, an uppercut at 100 μm should be made to prevent defectson the surface. The PSD was measured with 3.5 bar to rip apart particlesthat may have built agglomerates.

10 μm 13-20% 20 μm 34-42% 32 μm 50-60% 65 μm 80-90% 100 μm  99% d(0.1) 5-8 μm d(0.5) 26-32 μm d(0.9) 54-68 μm

Spraying Behavior

After sieving the powder, an anticaking agent (aluminumoxid 0.2%) shouldbe mixed into the formulation. The particles will build lessagglomerates and a better electrostatic charge could also be observed.

Spraying

Optitronic—Pistol Control Unit by Gema

After a lot of sprayed probes, this is the custom setting that proved tofunction very good for compositions according to the present invention.

High voltage [kV] 45 Current [μA] 20 Powder output Nm³/h] 90 Airflow[Nm³/h] 2.5

Curing Condition

200° C./15 min

Flexibility

Determine flexibility in accordance with ASTM 0522, method B using a 1.4inch mandrel. Spray the coating, according to manufacturers'recommendations, on a steel panel, tinplated 0.010 inches (0.0254 cm)thick. Examine the coating for cracks over the area of the bend.

Examples

Basic Formulations (Achievable Gloss Grades)

Samples 1-3 Acid Functional Resins

2 3 (Comparitive (Comparitive Example) Example) No. Constituent/SourceDescription Wt % Wt % Wt % Acrylic Resin Carboxyl functional acrylic33.00 Joncryl 822 AN resin BASF with an acid value of 70 mg KOH/g EW 802g/Eq Acrylic Resin Carboxyl functional acrylic 34.00 34.00 Joncryl 815AN resin BASF with an acid value of 40 mg KOH/g EW 1403 g/Eq PolyesterResin Carboxyl functional polyester 32.00 Crylcoat 2687-2 resin AllnexGroup with an acid value of 90 mg KOH/g EW 623 g/Eq Polyester ResinCarboxyl functional polyester 33.00 32.00 Crylcoat E 37179 resin AllnexGroup with an acid value of 70 mg KOH/g EW 802 g/Eq Crosslinking agentHydroxyalkylamide 5.50 5.50 8.0 Primid XL-552 Crosslinker EMS-GriltechCAS No. [6334-25-4] with an OH value of 660 mg KOH/g EW of 85 g/EqDegassing agent Benzoin 0.70 0.70 0.70 Benzoin CAS No. [119-53-9]Pigment Furnace carbon black 1.00 1.00 1.00 Raven 2000 Black (C.I.Pigment Black 6) Columbian Chemicals CAS No. [1333-86-4] Company,Georgia Pigment Iron oxide 2.37 2.37 2.37 Bayferrox 316 (C.I. PigmentBlack 11) Lanxess Inorganic Pigments, Germany CAS No. [1317-61-9] GlossControl agent Kaolinite 23.43 23.43 23.93 China Clay Extra ST CASNo.[00-1332-58-7] Kamig AG, Austria total 100.00 100.00 100.00

Samples 4-9 Hydroxyl Functional Resins

No. Constituent/Source Description Wt % Wt % Wt % Wt % Wt % Wt % 1Acrylic Resin Hydroxyl functional 26.00 26.00 26.00 27.00 Joncryl 587acrylic resin BASF with an OH value of 92 mg KOH/g EW 610 g/Eq 2 AcrylicResin Hydroxyl functional 27.00 27.5 AH-800SF acrylic resin Sun Polymerswith a hydroxyl Mooresville, Indiana value of 70 mg KOH/g EW 802 g/Eq 3Polyester Resin Hydroxyl polyester 12.0 Crylcoat 2814-0 with a hydroxylAllnex Group value 295 mg KOH/g EW 190 g/Eq 4 Polyester Resin Hydroxylfunctional 26.00 Crylcoat 2818-0 polyester resin Allnex Group with an OHvalue of 100 mg KOH/g EW 561 g/Eq 5 Polyester Resin Hydroxyl functional26.00 26.00 26.00 26.00 Crylcoat 2860 polyester resin Allnex Group withan OH value of 50 mg KOH/g EW 1122 g/Eq 6 Crosslinking agent Blocked20.00 18.00 20.00 32.5 Crelan NW 5 cycloaliphatic Covestro AGpolyisocyanate Leverkusen, with a total NCO Germany content of 12.7% EW333 g/Eq 7 Crosslinking agent Blocked 22.00 Crelan NW 5 cycloaliphatic+10% (to the polyisocyanate stoichiometry) with a total NCO content of12.7% EW 333 g/Eq 8 Crosslinking agent Blocked 18.00 Crelan NW 5cycloaliphatic −10% (to the polyisocyanate stoichiometry) with a totalNCO content of 12.7% EW 333 g/Eq 9 Degassing agent Benzoin 0.7 0.7 0.70.7 0.7 0.7 Benzoin CAS No. [119-53-9] 10 Pigment Furnace carbon black1.00 1.00 1.00 1.00 1.00 1.00 Raven 2000 Black (C.I. Pigment BlackColumbian 6) Chemicals CAS No. [1333-86- Company, Georgia 4] 11 PigmentIron oxide 2.37 2.37 2.37 2.37 2.37 2.37 Bayferrox 316 (C.I. PigmentBlack 11) Lanxess Inorganic Pigments, CAS No. [1317-61-9 Germany 12Gloss Control agent Kaolinite 23.93 21.93 25.93 23.93 23.93 23.93 ChinaClay Extra ST CAS No.[00-1332- Kamig AG, Austria 58-7] Total 100.00100.00 100.00 100.00 100.00 100.00

Gloss Results of Samples 1-8

7 8 (comparative (comparative Gloss 1 2 3 4 5 6 example) example) 9 20°1.3 7.0 6.0 2.0 2.0 1.7 5.0 12.0 0.8 60° 12.6 41.0 39.0 17.0 20.0 16.036.0 53.0 9 85° 24.0 74.0 56.0 35.0 56.0 39.0 72.0 75.0 20

DS2 Test Method (Chemical Resistance Test)

If one can see example 1 according to the invention, shows already agloss level of below 15 at 60°. Surprisingly it was found that the sameor nearly the same difference in acid value for acrylic resins (example2) or polyester resin (example 3) showed much higher gloss values. Whenhydroxyl functional polyester/polyester combinations where used (like inexample 8) even differences of more than 50 in the hydroxyl value led togloss level above 50. The formulation 7 according to the invention wherea difference in the OH-value of 22 lead to a gloss level of 35 at 60°was based on pure acrylic resins, however the flexibility of the coatingwas poor an early delamination of the coating from the substrate wasseen with bending. It was also seen that when formulations according tothe invention where used also changes of the stoichiometric content ofthe hardener led only to a slight change in the gloss (see example 4, 5and 6). With a preferred difference of functionality according to gloss,mechanics and chemical stability even gloss levels below 10 werepossible with hydroxyl functional polyester/acrylic resin(s) combinationlike shown in example 9. Furthermore it was found that thepolyester/polyester combinations showed a much better mechanicalperformance in respect to flexibility of the coating (like tested withMandrel bending with ¼ inch according to ASTM 0522 described in moredetails later on) especially compared to the acrylic/acryliccombinations. However, these polyester/polyester combination (likeexample 3) generally did not show as high chemical resistance like theacrylic/acrylic combinations. Surprisingly it was found that accordingto the invention via the combination of acrylic resin(s) and polyesterresin(s) with a difference of higher than 30 in the functional groupsshowed the right balance of mechanical and chemical properties.

In a special embodiment of the invention the powder coatings can evenfulfill the requirements of military applications like very low glosslevels, high chemical resistance, mechanical properties and mustard gastest. Further details can on that kind of requirements can be forexample found in MIL-PRF-32348. Especially the chemical agent resistancetest is of high importance. A suitable method to make a pre-test forthat kind of requirement the so called DS2 test.

The chemical resistance test with the DS2 contaminating agent simulatesthe Army Research Laboratory (ARL) methodology for contamination,against chemical warfare agents (CWA).

DS2 will neutralize all known toxic chemical agents.

The DS2 contamination agent contains 70% diethylenetriamine, 28%ethylene glycol monomethyl ether and 2% sodium hydroxide (3N).

One drop (1 to 2 mL) of the DS2 reagent was added to the surface of thefinal powder coating, the surface was covered with a watch glass and theDS2 reagent was left to attack the surface for 30 minutes at roomtemperature. The DS2 reagent was washed off with water. The evaluationcriteria for testing results are no brightening and swelling. Numericalvaluations ranging from 1 to 3 were assigned. 1 is the best performanceand 3 the poorest performance. To get rate 1, no surface changes must bevisible, for rate 2 only slight surface changes can be visible such assubtle brightening, for rate 3 strong brightening must occur.

Chemical Resistance Results of Samples 1-9

1 2 3 4 5 6 7 8 9 Value 3 Value 1 Value 3 Value 2 Value 2 Value 2 Value1 Value 2 Value 1

As can be seen in the example 1 to 9, generally there seems to be thetrend that carboxy functional acrylic/polyester combinations accordingto the invention showed not as good values like the hydroxyl functionalones. Example 2 and 7 (pure acrylic based system) showed good results onthe chemical test but was not sufficient in the mechanical flexibility.The best performance was seen in example 9 according to the inventionwhere the chemical stability could be reached together with a sufficientmechanical flexibility.

In particular the formulations 10 to 15 led to very good resultsaccording to the requirements for military applications.

Example 10: PFA Black Fed Std. 37030

No. Constituent/Source Description Wt % 1 Acrylic Resin Hydroxyl AcrylicResin 27.50 AH-800SF with a hydroxyl value of 70 mg KOH/g Sun PolymersEW 802 g/Eq Mooresville, Indiana 2 Polyester Resin Hydroxyl polyesterwith a hydroxyl value 12.00 Crylcoat 2814-0 295 mg KOH/g Allnex Group EW190 g/Eq 3 Crosslinking Agent Blocked cycloaliphatic polyisocyanate32.50 Crelan NW 5 with a total NCO content of 12.7% Covestro AG EW 333g/Eq Leverkusen, Germany 4 Flatting Agent2-Phenyl-2-Imidazoline-pyromellitate 2.70 Acetomer 68 CAS [54553-90-1]Aceto Corporation 5 Flatting Agent Dodecanedioic acid 0.90 DDDA CAS No.[693-23-2] Invista, Germany EW of 115 g/Eq 6 Texturing AgentFluoroethylene based agent 2.00 Lanco 1890 N CAS No. [9002-84-0]Lubrizol Ltd, UK 7 Flow Control Agent Carboxyl functional acrylic 1.00Resiflow P-64F flow control agent Worlee Chemie Estron Chemicals,Germany 8 Degassing Agent Benzoin 0.70 Benzoin CAS No. [119-53-9] 9Surface Modifier Semi-Crystalline 1.00 Hyflon PFA P7010 Perfluorinatedresin Solvay Specialty Polymers, Germany CAS No. [26655-00-5] 10 ImpactModifier Copolyester 2.70 Griltex ES 502 G EMS-Chemie AG, Suisse 11Pigment Furnace carbon black 0.99 Raven 2000 Black (C.I. Pigment Black6) Columbian Chemicals Company, Georgia CAS No. [1333-86-4] 12 PigmentIron oxide 2.37 Bayferrox 316 (C.I. Pigment Black 11) Lanxess InorganicPigments, Germany CAS No. [1317-61-9] 13 Gloss Control Agent Kaolinite13.64 China Clay Extra ST CAS No.[00-1332-58-7] Kamig AG, Austria Total100.00

Example 11: PFA Green Fed Std. 34094

No. Constituent/Source Description Wt % 1 Acrylic Resin Hydroxyl AcrylicResin 27.50 AH-800SF with a hydroxyl value of 70 mg KOH/g Sun PolymersEW 802 g/Eq Mooresville, Indiana 2 Polyester Resin Hydroxyl polyesterwith a hydroxyl value 12.00 Crylcoat 2814-0 295 mg KOH/g Allnex Group EW190 g/Eq 3 Crosslinking Agent Blocked cycloaliphatic polyisocyanate32.50 Crelan NW 5 with a total NCO content of 12.7% Covestro AG EW 333g/Eq Leverkusen, Germany 4 Flatting Agent2-Phenyl-2-Imidazoline-pyromellitate 2.70 Acetomer 68 CAS [54553-90-1]Aceto Corporation 5 Flatting Agent Dodecanedioic acid 0.90 DDDA CAS No.[693-23-2] Invista, Germany EW of 115 g/Eq 6 Texturing AgentFluoroethylene based agent 2.00 Lanco 1890 N CAS No. [9002-84-0]Lubrizol Ltd, UK 7 Flow Control Agent Carboxyl functional acrylic 1.00Resiflow P-64F flow control agent Worlee Chemie Estron Chemicals,Germany 8 Degassing Agent Benzoin 0.70 Benzoin CAS No. [119-53-9] 9Surface Modifier Semi-Crystalline 1.00 Hyflon PFA P7010 Perfluorinatedresin Solvay Specialty Polymers, Germany CAS No. [26655-00-5] 10 ImpactModifier Copolyester 2.70 Griltex ES 502 G EMS-Chemie AG, Suisse 11Pigment Bismuth vanadate 0.65 Duropal Yellow 6218 (C.I. Pigment Yellow184) Habich, Austria CAS No. [14059-33-7] 12 Pigment Iron Oxide 2.35Bayferrox 943 (C.I. Pigment Yellow 42) Lanxess Inorganic Pigments,Germany CAS No. [20344-49-4] 13 Pigment Chromium oxide 5.95 ColorthermGreen GN (C.I. Pigment Green 17) Lanxess Inorganic Pigments, Germany CASNo. [1308-38-9] 14 Pigment Iron oxide 3.00 Bayferrox 316 (C.I. PigmentBlack 11) Lanxess Inorganic Pigments, Germany CAS No. [1317-61-9] 15Pigment Rutile Titanium Dioxide 0.22 Kronos 2310 (C.I. Pigment White 6)Kronos International Inc. CAS No. [13463-67-7] 16 Rheological AdditiveOrganic derivative of a smectite clay 3.00 Bentone SD-3 CAS No.[121888-67-3] Elementis Specialties 17 Gloss Control Agent Kaolinite1.83 China Clay Extra ST CAS No.[00-1332-58-7] Kamig AG, Austria Total100.00

Example 12: PFA Tan Fed Std. 33446

No. Constituent/Source Description Wt % 1 Acrylic Resin Hydroxyl AcrylicResin 26.70 AH-800SF with a hydroxyl value of 70 mg KOH/g Sun PolymersEW 802 g/Eq Mooresville, Indiana 2 Polyester Resin Hydroxyl polyesterwith a hydroxyl value 12.00 Crylcoat 2814-0 295 mg KOH/g Allnex Group EW190 g/Eq 3 Crosslinking Agent Blocked cycloaliphatic polyisocyanate31.00 Crelan NW 5 with a total NCO content of 12.7% Covestro AG EW 333g/Eq Leverkusen, Germany 4 Flatting Agent2-Phenyl-2-Imidazoline-pyromellitate 2.70 Acetomer 68 CAS [54553-90-1]Aceto Corporation 5 Flatting Agent Dodecanedioic acid 0.90 DDDA CAS No.[693-23-2] Invista, Germany EW of 115 g/Eq 6 Texturing AgentFluoroethylene based agent 2.00 Lanco 1890 N CAS No. [9002-84-0]Lubrizol Ltd, UK 7 Flow Control Agent Carboxyl functional acrylic 1.00Resiflow P-64F flow control agent Worlee Chemie Estron Chemicals,Germany 8 Degassing Agent Benzoin 0.70 Benzoin CAS No. [119-53-9] 9Surface Modifier Semi-Crystalline 1.00 Hyflon PFA P7010 Perfluorinatedresin Solvay Specialty Polymers, Germany CAS No. [26655-00-5] 10 ImpactModifier Copolyester 2.70 Griltex ES 502 G EMS-Chemie AG, Suisse 11Pigment Iron Oxide 0.83 Colortherm Yellow 10 (C.I. Pigment Yellow 42)Lanxess CAS No. [51274-00-1] 12 Pigment Iron Oxide 1.13 Bayferrox 3920(C.I. Pigment Yellow 42) Lanxess CAS No. [51274-00-1] 13 Pigment IronOxide 0.41 Bayferrox 130 B (C.I. Pigment Red 101) Lanxess CAS No.[1309-37-1] 14 Pigment Chromium Oxide 1.00 Colortherm Green GN (C.I.Pigment Green 17) Lanxess CAS No. [1308-38-9] 15 Pigment Rutile TitaniumDioxide 12.83 Kronos 2310 (C.I. Pigment White 6) Kronos InternationalInc. CAS No. [13463-67-7] 16 Rheological Additive Organic derivative ofa smectite clay 3.00 Bentone SD-3 CAS No. [121888-67-3] ElementisSpecialties 17 Gloss Control Agent Kaolinite 0.10 China Clay Extra STCAS No.[00-1332-58-7] Kamig AG, Austria Total 100.00

Example 13: PTFE Black Fed Std. 37030

No. Constituent/Source Description Wt % 1 Acrylic Resin Hydroxyl AcrylicResin 27.50 AH-800SF with a hydroxyl value of 70 mg KOH/g Sun PolymersEW 802 g/Eq Mooresville, Indiana 2 Polyester Resin Hydroxyl polyesterwith a hydroxyl value 12.00 Crylcoat 2814-0 295 mg KOH/g Allnex Group EW190 g/Eq 3 Crosslinking Agent Blocked cycloaliphatic polyisocyanate32.50 Crelan NW 5 with a total NCO content of 12.7% Covestro AG EW 333g/Eq Leverkusen, Germany 4 Flatting Agent2-Phenyl-2-Imidazoline-pyromellitate 2.70 Acetomer 68 CAS [54553-90-1]Aceto Corporation 5 Flatting Agent Dodecanedioic acid 0.90 DDDA CAS No.[693-23-2] Invista, Germany EW of 115 g/Eq 6 Texturing AgentFluoroethylene based agent 2.00 Lanco 1890 N CAS No. [9002-84-0]Lubrizol Ltd, UK 7 Flow Control Agent Carboxyl functional acrylic 1.00Resiflow P-64F flow control agent Worlee Chemie Estron Chemicals,Germany 8 Degassing Agent Benzoin 0.70 Benzoin CAS No. [119-53-9] 9Surface Modifier Polytetrafluorethylene 1.00 Fluoropolymer CAS No.[9002-84-0] Dyneon TFM 1750 PTFE, Dyneon 10 Impact Modifier Copolyester2.70 Griltex ES 502 G EMS-Chemie AG, Suisse 11 Pigment Furnace carbonblack 0.99 Raven 2000 Black (C.I. Pigment Black 6) Columbian ChemicalsCompany, Georgia CAS No. [1333-86-4] 12 Pigment Iron oxide 2.37Bayferrox 316 (C.I. Pigment Black 11) Lanxess Inorganic Pigments,Germany CAS No. [1317-61-9] 13 Gloss Control Agent Kaolinite 13.64 ChinaClay Extra ST CAS No.[00-1332-58-7] Kamig AG, Austria Total 100.00

Example 14: PTFE Green Fed Std. 34094

No. Constituent/Source Description Wt % 1 Acrylic Resin Hydroxyl AcrylicResin 27.50 AH-800SF with a hydroxyl value of 70 mg KOH/g Sun PolymersEW 802 g/Eq Mooresville, Indiana 2 Polyester Resin Hydroxyl polyesterwith a hydroxyl value 12.00 Crylcoat 2814-0 295 mg KOH/g Allnex Group EW190 g/Eq 3 Crosslinking Agent Blocked cycloaliphatic polyisocyanate32.50 Crelan NW 5 with a total NCO content of 12.7% Covestro AG EW 333g/Eq Leverkusen, Germany 4 Flatting Agent2-Phenyl-2-Imidazoline-pyromellitate 2.70 Acetomer 68 CAS [54553-90-1]Aceto Corporation 5 Flatting Agent Dodecanedioic acid 0.90 DDDA CAS No.[693-23-2] Invista, Germany EW of 115 g/Eq 6 Texturing AgentFluoroethylene based agent 2.00 Lanco 1890 N CAS No. [9002-84-0]Lubrizol Ltd, UK 7 Flow Control Agent Carboxyl functional acrylic 1.00Resiflow P-64F flow control agent Worlee Chemie Estron Chemicals,Germany 8 Degassing Agent Benzoin 0.70 Benzoin CAS No. [119-53-9] 9Surface Modifier Polytetrafluorethylene 1.00 Fluoropolymer CAS No.[9002-84-0] Dyneon TFM 1750 PTFE, Dyneon 10 Impact Modifier Copolyester2.70 Griltex ES 502 G EMS-Chemie AG, Suisse 11 Pigment Bismuth vanadate0.65 Duropal Yellow 6218 (C.I. Pigment Yellow 184) Habich, Austria CASNo. [14059-33-7] 12 Pigment Iron Oxide 2.35 Bayferrox 943 (C.I. PigmentYellow 42) Lanxess Inorganic Pigments, Germany CAS No. [20344-49-4] 13Pigment Chromium oxide 5.95 Colortherm Green GN (C.I. Pigment Green 17)Lanxess Inorganic Pigments, Germany CAS No. [1308-38-9] 14 Pigment Ironoxide 3.00 Bayferrox 316 (C.I. Pigment Black 11) Lanxess InorganicPigments, Germany CAS No. [1317-61-9] 15 Pigment Rutile Titanium Dioxide0.22 Kronos 2310 (C.I. Pigment White 6) Kronos International Inc. CASNo. [13463-67-7] 16 Rheological Additive Organic derivative of asmectite clay 3.00 Bentone SD-3 CAS No. [121888-67-3] ElementisSpecialties 17 Gloss Control Agent Kaolinite 1.83 China Clay Extra STCAS No.[00-1332-58-7] Kamig AG, Austria Total 100.00

Example 15: PTFE Tan Fed Std. 33446

No. Constituent/Source Description Wt % 1 Acrylic Resin Hydroxyl AcrylicResin 26.70 AH-800SF with a hydroxyl value of 70 mg KOH/g Sun PolymersEW 802 g/Eq Mooresville, Indiana 2 Polyester Resin Hydroxyl polyesterwith a hydroxyl value 12.00 Crylcoat 2814-0 295 mg KOH/g Allnex Group EW190 g/Eq 3 Crosslinking Agent Blocked cycloaliphatic polyisocyanate31.00 Crelan NW 5 with a total NCO content of 12.7% Covestro AG EW 333g/Eq Leverkusen, Germany 4 Flatting Agent2-Phenyl-2-Imidazoline-pyromellitate 2.70 Acetomer 68 CAS [54553-90-1]Aceto Corporation 5 Flatting Agent Dodecanedioic acid 0.90 DDDA CAS No.[693-23-2] Invista, Germany EW of 115 g/Eq 6 Texturing AgentFluoroethylene based agent 2.00 Lanco 1890 N CAS No. [9002-84-0]Lubrizol Ltd, UK 7 Flow Control Agent Carboxyl functional acrylic 1.00Resiflow P-64F flow control agent Worlee Chemie Estron Chemicals,Germany 8 Degassing Agent Benzoin 0.70 Benzoin CAS No. [119-53-9] 9Surface Modifier Polytetrafluorethylene 1.00 Fluoropolymer CAS No.[9002-84-0] Dyneon TFM 1750 PTFE, Dyneon 10 Impact Modifier Copolyester2.70 Griltex ES 502 G EMS-Chemie AG, Suisse 11 Pigment Iron Oxide 0.83Colortherm Yellow 10 (C.I. Pigment Yellow 42) Lanxess CAS No.[51274-00-1] 12 Pigment Iron Oxide 1.13 Bayferrox 3920 (C.I. PigmentYellow 42) Lanxess CAS No. [51274-00-1] 13 Pigment Iron Oxide 0.41Bayferrox 130 B (C.I. Pigment Red 101) Lanxess CAS No. [1309-37-1] 14Pigment Chromium Oxide 1.00 Colortherm Green GN (C.I. Pigment Green 17)Lanxess CAS No. [1308-38-9] 15 Pigment Rutile Titanium Dioxide 12.83Kronos 2310 (C.I. Pigment White 6) Kronos International Inc. CAS No.[13463-67-7] 16 Rheological Additive Organic derivative of a smectiteclay 3.00 Bentone SD-3 CAS No. [121888-67-3] Elementis Specialties 17Gloss Control Agent Kaolinite 0.10 China Clay Extra ST CASNo.[00-1332-58-7] Kamig AG, Austria Total 100.00

Gloss Results of Samples 10-15

Gloss 10 11 12 13 14 15 20° 0.1 0.1 0.2 0.1 0.2 0.7 60° 1.0 0.8 0.8 1.01.0 0.9 85° 1.3 1.0 0.8 1.2 0.9 0.9

Chemical Resistance Results of Samples 10-15 According to the DS2 Test.

10 11 12 13 14 15 Value 1 Value 1 Value 1 Value 1 Value 1 Value 1

What is claimed is:
 1. A curable powder coating composition comprising:one or more hydroxyl or carboxyl functional polyester(s) (A) in anamount of 9-90 weight percent based on the overall powder coatingcomposition, the functional polyester(s) (A) being characterized by a Tgof more than 35° C.; one or more hydroxyl or carboxyl functional acrylicresin(s) (B) in an amount of 9-90 weight percent based on the overallpowder coating composition, the hydroxyl or carboxyl functional acrylicresin(s) (B) being characterized by a Tg of more than 35° C.; and one ormore cross linker(s) (C) able to react with (A) and/or (B) in an amountof 1-50 weight percent based on the overall powder coating composition,wherein the hydroxyl- or acid-value of (A) and (B), or if a mixture ofpolyesters (A) and/or a mixture of acrylic resins (B) is present, theaverage hydroxyl- or acid-value of the mixture of the polyesters (A)and/or the mixture of acrylic resins (B), have a difference of higherthan or equal to 20, and wherein the weight ratio of (B)/(A) is between1.0 and 4.5.
 2. The powder coating composition according to claim 1,wherein (B) has a hydroxyl value or an average hydroxyl value of morethan or equal to
 40. 3. The power coating composition according to claim1, wherein (A) has a hydroxyl value or an average hydroxyl value of morethan or equal to
 200. 4. The powder coating composition according toclaim 1, additionally comprising one or more fluoro containing organiccompounds (D).
 5. The powder coating composition according to claim 4,wherein the one or more fluoro containing organic compounds (D) arefluoro containing oligomers and/or polymers in a concentration ofbetween 0.5 and 19 weight percent based on the sum of (A), (B), and (D).6. The powder coating composition according to claim 1, wherein (C)comprises isocyanate based hardeners.
 7. The powder coating compositionaccording to claim 6, wherein the isocyanate based hardener is a blockedisocyanate based hardener.
 8. The powder coating composition accordingto claim 7, wherein the blocked isocyanate based hardener is acaprolactam blocked isocyanate based hardener.
 9. The powder coatingcomposition according to claim 6, wherein the isocyanate based hardeneris present in a weight concentration of more than or equal to 50% of(C).
 10. The powder coating composition according to claim 1, wherein(C) comprises one or more carboxylic acid(s) and/or salt(s) ofcarboxylic acid(s) containing hardeners present in aweight-concentration of below or equal to 50% of (C).
 11. The powdercoating composition according to claim 7, wherein (C) comprisesdodecanedioic acid and/or pyromellitic groups.
 12. The powder coatingcomposition according to claim 1, wherein (D) comprises perfluoroalkoxyand/or PTFE compounds.
 13. The powder coating composition according toclaim 1, additionally comprising a polymer with a melting area of 50° C.to 200° C. and a viscosity of 10 to 500 Pas, measured with plate/plateviscometer at a shear rate of 10 rad/s.
 14. The powder coatingcomposition according to claim 4, wherein the one or more fluorocontaining organic compounds (D) are fluoro containing oligomers and/orpolymers in a concentration of between 1.5 and 3.5 weight percent basedon the sum of (A), (B), and (D), and the polymer is a polyester basedand/or acrylic based material.
 15. The powder coating compositionaccording to claim 1, wherein the powder coating additionally comprisesphyllosilicates in a weight-concentration of between 3 and 30 weightpercent based on the overall powder coating composition.
 16. The powdercoating composition according to claim 15, wherein the phyllosilicate isselected from the group comprising china clay, smectite clay, theirderivatives or organic derivatives, and mixtures thereof.
 17. The powdercoating composition according to claim 1, wherein the applied powdercoating composition has a gloss level of equal or below 20 measured at60°.